1. Field of the Invention
The present invention relates to an apparatus for preventing a grinding wheel from rotating at an excessive circumferential speed, more than a predetermined speed, due to an improper selective use of belt pulleys.
2. Description of the Prior Art
In grinding technology, generally, a motor pulley on a motor axis is exchanged with a reserved motor pulley having a large diameter, thereby to recover a circumferential speed of a grinding wheel when the same wears to one-half of its useable range. However, unless the motor pulley held in reserve is exchanged with the previously used motor pulley having a small diameter when the grinding wheel wears beyond the useable or tolerable range and is to be exchanged with a fresh grinding wheel, it results that the fresh grinding wheel is rotated at an excessive speed more than a predetermined speed. An apparatus for preventing circumferential overspeeding of a grinding wheel is well known in which only a small motor pulley can be attachable to a drive motor while a grinding wheel with a large diameter, such as a fresh grinding wheel, is being mounted upon a wheel spindle, and such an apparatus has already been applied to a universal type grinding machine in which a grinding wheel is attachable to both ends of a wheel spindle.
Such an apparatus for the universal grinding machine is provided at both sides of the wheel head with pivotal arms having rejection pins which are respectively opposed to the grinding wheel and the motor pulley. However, the arms are somewhat extended to present the rejection pins into such positions as to respectively closely face the grinding wheel and the motor pulley and, when pivoted, they effect long distance movements on the rejection pins. For this reason, the apparatus is inadequate in mechanism to the harmonization with the pulley cover assembly and raises a problem in accommodating the arms within the pulley cover assembly. Especially, as long as a closed type pulley cover assembly is employed, which is closed also at its inside portion facing one side of the wheel head, the foregoing known apparatus for preventing circumferential overspeeding of a grinding wheel cannot be utilized in coexistence therewith.